mobs such as slimes, ghasts, magma cubes, baby mobs, and few more are not able to push other mobs out of the way and also they cant push players (none of the mobs are able to push players). I'm pretty sure it's a bug because this doesn't happen with mobs such as cows and pigs they can push each other out but not a huge majority of the mobs. fixing this issue could allow some really interesting mob farm designs. thank you